Electrical musical instrument



July 7, w E K ELECTRICAL MUSICAL INSTRUMENT Filed Dec. 6, '1933 2 Sheets-Sheet l FREQUENCY [23232: AMPLIFIER m INVENTOR:

July 7, 1936. w. E. KOCK 2,046,463

7 ELECTRICAL MUSICAL INSTRUMENT Filed Dec. 6, 1933 2 Sheets-Sheet 2 AMPuHEIg 3 g y am K K K B FIG. 9

A I To GLOW LAMP CIQCUITS F16. 0 INVENTQQ:

WM'MZ XML Patented July 7, 1936 PATENT OFFICE 2,046,452 ELECTRICAL MUSICAL INSTRUMENT Winston Edward Keck, Berlin, Germany, assignor to The Baldwin Company, Cincinnati, Ohio Application December 6, 1933, Serial No. 701,173 In Germany October 6, 1933 11 Claims.

This invention relates to electrical musicalin struments of the type embodying an electrical vibrating system for the production of sound. It aims to provide a novel method for the generation of the electrical oscillations which produce the sound and to this end it provides an intermittent glow discharge oscillating circuit of new and improved design in connection with a source of current and a sound producing contrivance.

One advantage of the new oscillating circuit is that the pitch of the generated oscillation is practically independent of the electromotive force of the source of current over a wide range of variation, that is to say, the pitch of the generated oscillation is not noticeably affected by comparatively large variations of the supply voltage. This overcomes the drawback of previous instruments using thermionic tubes or glow dis charge lamps wherein the production of oscillations of adequate pitch was impossible without a constant supply voltage.

Another advantage of the new oscillating circult is that several oscillations, each possessing a different wave form and hence a different tone quality, are simultaneously produced. For example, one of the oscillations is practically sinusoidal so that a very pure tone results. Heretofore it has been impossible to obtain directly from an ordinary intermittent glow discharge oscillator, an oscillation of such purity.

Also, in previous glow discharge oscillating circuits, variations in the characteristics of the glow discharge lamp itself caused a noticeable change in the frequency of oscillation; in the new circuit, ordinary variations in the glow discharge lamp do not noticeably afiect the frequency.

The new circuit, which shall hereinafter be re ferred to as the inductive glow discharge oscillator, is obtained by placing an inductance in any one of several positions in the circuit of an intermittent glow discharge oscillator. Certain simple adjustments, the details -.f which will be described later, are then required to effect the desired result, namely, the maintenance of a constant pitch, and the production of several distinctive wave forms.

By the use of the term constant frequency I do not imply the term fixed frequency, for although the frequency may be relatively constant with respect to certain variables in the circuit, namely, for example, supply voltage and tube characteristics, it is nevertheless possible to vary the frequency by altering other variables in the circuit, for example, the inductance or the capacity.

Inductances, such as transformers, have previously been inserted in glow discharge oscillating circuits used for musical instruments and the like, but in such cases the inductance served merely as a means of transferring the oscillations to an amplifier or the like, or for various other reasons. However, it has not heretofore been suggested to use an inductance as an integral and essential part of the glow discharge oscillator itself in order to attain oscillations of greater constancy or purity or variety of wave form.

Fairly pure oscillations have been obtained from a glow lamp operating in a manner similar to that of the oscillating or singing electric arc, but the production of pure vibrations by means of a truly intermittent glow discharge has not been recorded.

In the diagrams:

Figs. 1, 3, 4, and 5 show various ways of inserting the inductance to obtain the desired results.

Fig. 2 portrays a graph of the frequency-voltage characteristics of the two types of glow dis charge oscillators.

Fig. 6 illustrates the application of the principle to a thyratron oscillator.

Fig. 7 shows the utilization of several wave forms.

Fig. 8 illustrates three circuits in combination.

Fig. 9 shows how different notes may be produced by one circuit.

Fig. 10 shows a method of producing a tremolo effect.

Referring now to Fig. 1, B is a battery or other source of direct current, in a. circuit containing a resistance R, an inductance L, a condenser, C, and a sound producing contrivance T, which may be a telephone, loudspeaker, amplifier or the like.

G is a glow discharge lamp of either the hot or cold cathode type.

The condenser C may be designed for .0001 to 40 2 microfarads, the resistance R for .01 to 10 megohms, the inductance L for 30 to 1000 henries and the battery B, a voltage of 60 to 250 volts.

The condenser C is charged from the current source through the resistance R and inductance L and when the voltage across the terminals of the lamp G has attained the ignition potential of the lamp, the charge residing on the plates of the condenser is discharged thru the inductance and the lamp. The discharges follow each other in rapid succession through the tube, the frequency of the discharge, and hence the pitch of the sound produced, being determined by the constants of the circuit in the following manner: at a low value of the supply voltage, the frequency is also low and is a function of the resistance, the supply voltage, the capacity, the tube characteristics, and, to some extent, the inductance. However, as the voltage is increased, the frequency does not increase proportionately, but

approaches asymptotically a limiting value, which value is dependent only on the inductance, capacity, and glow discharge tube, and corresponds approximately to the resonant frequency as determined by the inductance, capacity, and characteristics of the glow discharge tube.

v In the light of these teachings, it will be within the skill of the worker in the art to produce stable oscillating circuits operating at desired frequencies. By way of example, and with reference to the values shown above, with a given neon tube, having an ignition voltage of about 100 volts, in a circuit such as that shown in Fig. 1, comprising an inductance of 100 henries, a condenser of .005 microfarads, and a resistance of megohm, and an impressed voltage in the neighborhood of 200 volts, oscillations were produced of a frequency of 256, corresponding to middle C; and the oscillations remained at this frequency in spite of substantial variations in the impressed voltage. Variations in these values may be made to attain different frequencies, and to adapt my teachings to glow discharge devices of differing characteristics.

I have attained what I believe to be a novel effect in oscillating circuits employing glow tubes,namely, an effect of stability, such that unintentional variations in the energy supply do not produce frequency variations detectable by the ear. I accomplish this effect by providing a supply circuit for the glow discharge device including a resistance, and a control circuit therefor which is tuned to a desired frequency by capacity and inductance, and then operating the system in a voltage range in which the resonance of the control circuit fixes the frequency of the oscillations.

Fig. 2 portrays this phenomenon graphically. Curve 1 shows the variation of frequency with voltage in the ordinary glow discharge oscillator, i. e. no inductance present. Curve 2 shows the variation of frequency with voltage of the inductive glow discharge oscillator, the circuit of Fig. 1. With no inductance inthe circuit, as the supply voltage is increased, the frequency follows curve I, continually increasing to a very high frequency. However, when an inductance is inserted in the circuit as shown in Fig. 1, as the supply voltage is then increased, the frequency follows curve 2, and does not increase indefinitely as in the first case, but rather approaches asymptotically a frequency which is dependent only on the inductance, capacity, and glow discharge tube. This resonant frequency may also be referred to as the limiting frequency, as the curve approaches this frequency as a limit. However, this is not necessarily the highest frequency which can be produced with the given circuit. It often happens that as the voltage is further and further increased, the frequency finally jumps to a very high value, probably due to the fact that the inductance acts as a capacity, its distributed capacity and the capacity of the condenser in series yielding a value which affects the production of the very high frequency observed. For this reason, the term limiting frequency will hereinafter signify that frequency which the curve 2 approaches asymptotically and not the maximum frequency obtainable.

A comparison of these two curves shows that the inductance is the controlling factor in maintaining a constant frequency. Upon this controlling inductance rest all the effects which make this circuit an improvement over previous glow discharge circuits. 5

Over the portion X-X of curve 2, the slope is almost flat, and when the circuit is operated in this region, the frequency of oscillation is practically constant for wide variations in voltage. Further, when this condition is effected, the wave form of the alternating voltage across the condenser C becomes very nearly sinusoidal, although the current in the sound producing contrivance is still rich in harmonics. The voltage across the inductance possesses still another wave 15 form, likewise rich in harmonics, and the various currents in the circuit possess various wave forms. It is possible to utilize each of these wave forms independently or in connection with others. Possible methods will be described later.

As already mentioned, inductances have been inserted in electrical musical instruments of the glow discharge type for the purpose of transferring the oscillations to the amplifier or sound producing contrivance. These inductances were 26 of such comparatively small size, that, for the frequency region employed, they did not noticeably affect the pitch stability or the various wave forms. In other words, the operating regions of these instruments corresponded to the portion of the curve Y-Y, where the characteristics of the ordinary glow discharge oscillator and the inductive glow discharge oscillator are still very similar. However, operation on the flat, or gradually sloping (exclusive of the portion 35 YY), part of the curve, that is to say, the use of a controlling inductance, has not previously been recorded.

Figures 3, ,4, and 5 show various other ways of inserting the inductance to effect the desired result. It is noticed that the desired effect is obtained when the inductance and capacity are located in connection with the glow lamp so as to form a tuned controlling circuit therefor. The reason is that the inductance has the effect of holding back the sudden flow of current when the condenser charges or discharges through the glow lamp. It is also evident that, in many cases, the sound producing contrivance could also be made to serve as the controlling inductance. For example, in Fig. 4, if the sound producing contrivance, T, were designed with suificiently high inductance, it could serve as the controlling inductance, and the inductance L be dispensed with.

Fig. 6 shows how the principle may be applied to a thyratron glow discharge lamp type of oscillator in order to effect a more adequate pitch constancy and a plurality of wave forms. Variations similar to those for the circuit of the simple glow lamp, are also possible for this type of glow lamp.

Fig. 7 shows one method of utilizing several wave forms of the inductive glow discharge oscillator simultaneously or separately. Here the secondary S of transformer T2 is the controlling inductance. The sinusoidal voltage wave across C is fed into amplifier No. 1, the voltage generated in the secondary S of transformer T1 is fed into amplifier No. 2, and that generated in the primary P of transformer T2 is fed into a third amplifier. If desired, these amplifiers may be combined into one. The important point is that the three waves are different and each" will impart a diiferent tone color or timbre. By switching arrangements, each tone quality can be heard separately or simultaneously with the other tone qualities. Incidentally, this illustrates an example wherein the controlling inductance is a part of the sound producing contrivance, which in this case is amplifier No. 1

Inasmuch as the inductive glow discharge oscillater produces oscillations of a high degree of pitch constancy, this circuit is advantageously applied to instruments of the electric organ type. In a monophonic instrument, uncontrollable pitch variations, though objectionable, can be tolerated to some extent. However, in an instrument such as an electric organ, constancy of pitch is a necessity.

Fig. 8 shows one arrangement wherein the inductive glow discharge oscillator may be utilized in an electric organ. For clarity, only three circuits are shown. However, as many as eighty or more circuits could be easily included in an organ of this type without prohibitive space requirements. Each circuit contains its own resistance, inductance, capacity, and. glow lamp, although one source of current and one amplifier may be made to serve for the entire organ. The switches S1,S2, S3, may be operated by keys similar to those of a piano. For each circuit, the inductance and capacity are chosen so as to make 'the fiat portion of the frequency-voltage curve coincide with the necessary frequency for that particular note of the musical scale. This may be done either by careful selection of the condensers and inductances, or by having either the inductances or condensers variable. To make certain that the circuits are operating on the proper portion of their curve, final adjustments may be made by varying the voltage on the circuit by means of the potentiometer P. It is noticed that inasmuch as each circuit is complete, the tubes will begin to oscillate as soon as the voltage is applied. However, in order to hear musical notes from the sound producing contrivance, switches S1, S2, S3, must be depressed. Thus, when switch S1 is closed, the alternating voltage across the resistance R1 is impressed across the transformer T, and a note is heard in the loud speaker. When other switches are depressed, other notes are heard and an organ effect is thus duplicated.

The advantage of this method of operation is that the circuits are continually operating, and any change in characteristics that the glow lamp may undergo, occurs only for a short time after the voltage is applied. They soon reach a stable state and a very constant pitch is then maintained.

By choosing the value of R1, R2, R3, erly, the volume of the various notes can be equalized and a well voiced scale can be produced.

Changes in tone quality can be efiected by various adjustments in the amplifier, by distorting and altering the wave forms of the amplified oscillations. Various types of loud speakers may be employed in order to produce tone color variety. The various wave forms originally present in the oscillating circuit itself may be made use of, as previously described.

The volume of sound maybe controlled by means of adjustments in the amplifier.

Due to its pitch constancy, the inductive glow discharge oscillator is an advantageous oscillation generator likewise for monophonic instruments.

The usual procedure in previous monophonic glow discharge instruments has been to vary the pitch until the next discharge takes place.

by varying the resistance in the glow discharge circuit. However, when an inductive glow dis- I charge oscillator is properly operating, changes -key K2 is depressed, then both R2 and C1 are disconnected and a higher pitched note results.

A similar arrangement except that a plurality of inductances are used and only one condenser, is also possible.

Fig. 10 shows an arrangement by means of which a tremolo effect may be introduced into a monophonic or organ type instrument. An inductive glow discharge oscillator of very low frequency, one to fifteen cycles per second, is employed, and the voltage across the condenser C is impressed into an amplifier circuit. The plate resistance of the last tube of this amplifier forms part of the resistance of the potentiometer P from which the oscillating circuits on the organ are supplied with voltage. Whenswitch S is closed, a low frequency oscillating voltage is impressed on the grid of the last tube, and. the plate to filament resistance of this tube varies periodically. This causes the voltage on the potentiometer to vary, and the frequency of the glow lamp circuits experiences a tremolo effect. Due to the flatness of the voltage frequency characteristic curve, a large voltage change is required to produce a pleasing tremolo eiiect. Due to its purity, this slowly varying voltage is advantageously used to control the volume of the amplifier, so that a smooth volume tremolo is also easily obtainable.

By means of the inductive glow discharge oscillator, an effect similar to a inarimba or xylophone may be produced. The voltage across the resistance of a low frequency (a few cycles per second) inductive oscillator is made to affect the grid of one of the amplifier tubes which handles the notes of the entire instrument. This voltage varies as follows: When the discharge takes place, it has a very high value. It then gradually decreases to a low value until the next discharge takes place, at which time this voltage suddenly jumps to its high value again. The effect of this voltage on the grid of the amplifier tube is to cause the amplifier to suddenly have a very high amplification factor, gradually decreasing A single discharge would thus give the efiect of a bell. Discharges in rapid succession would produce the cfiect of a marimba or Xylophone. 1

It is to be understood that the invention is not limited to the specific arrangements shown, as obvious modifications will occur to a person skilled in the art. No limitations are intended beyond those set forth in the appended claims. In these claims no selection of any particular modification of the invention is intended to the exclusion of other modifications thereof, and the right to subsequently make claim to any modification not covered by these claims is expressly reserved.

I claim:

1. An electrical musical instrument comprising oscillating means which include a glow discharge device, a feed circuit therefor, and a resonant controlling circuit therefor, said feed circuit comprising a resistance and said resonant circuit comprising capacity and inductance, said resonant circuit being tuned to resonate at an audio frequency.

2. An electrical musical instrument comprising oscillating means which include a glow discharge device, a feed circuit therefor, a resonant controlling circuit therefor, and a sound produc ing device including inductance, said feed circuit comprising a resistance, and said resonant circuit comprising both capacity and inductance, said resonant circuit being tuned to resonate at an audio frequency, and the inductance of said sound producing device forming part, at least, of said inductance of said resonant circuit.

3. An electrical musical instrument comprising oscillating means which include a glow discharge device, a feed circuit therefor, a resonant controlling circuit therefor, a sound producing device including inductance, said feed circuit comprising a resistance, said resonant circuit comprising both capacity and inductance, said resonant circuit being tuned to resonate at an audio frequency, the inductance of said sound producing device forming part, at least, of said inductance of said resonant circuit, and means for varying the value of said capacity to vary the frequency of said oscillating means- 4. In an electrical musical instrument, a plurality of oscillating circuits each comprising a glow discharge device, a feed circuit therefor and a control circuit therefor, a common, closed current supply for said feed circuits, said control circuits being closed, whereby said oscillating circuits are kept in continuous oscillation during operation of said instrument, an output circuit having two leads, one lead connected to said several control circuits, said control cir-' cuits each containing a resistance, and means for selectively connecting the other lead of said output circuit to said control circuits at the op posite sides of said resistances so that voltages developed across said resistances respectively may be selectively impressed on said output circuit.

5. In an electrical musical instrument, a plurality of oscillating circuits each comprising a glow discharge device, a feed circuit therefor and a control circuit therefor, a common, closed, current supply for said feed circuits, said control circuits being closed, whereby said oscillating circuits are kept in continuous oscillation during operation of said instrument, an output circuit having two leads, one lead connected to said several control circuits, said control circuits each containing a resistance, means for selectively connecting the other lead of said output circuit to said control circuits at the opposite sides of said resistances so that voltages developed across said resistances respectively may be selectively impressed on said output circuit.

6. In an electrical musical instrument, a

plurality of oscillating circuits each comprising a glow discharge device, a feed circuit therefor and a control circuit therefor, a common, closed current supply for said feed circuits, said control circuits being closed, whereby said oscillating circuits are kept in continuous oscillation during operation of said instrument, an output circuit having two leads, one lead connected to said several control circuits, said control circuits each containing a resistance, means for selectively connecting the other lead of said output circuit to said control circuits at the opposite sides of said resistances so that voltages developed across said resistances respectively may be selectively impressed on said output circuit, a resistance bridging said current supply, and means for connecting said feed circuits selectively into said resistance.

7. In an electrical musical instrument, an electric oscillator of audible frequency, and an electrical oscillator of sub-audible frequency periodically affecting the pitch of the emitted notes of said instrument.

8. In an electrical musical instrument, a

plurality of oscillating means, means for proaudio frequency,'amplifying means for energy derived therefrom, and means for causing said amplified energy to vary the frequencies of said first mentioned oscillating means.

10. In an electrical musical instrument, a plurality of oscillating circuits having a common connection to a source of energy supply, said common connection including a thermionic tube, another oscillating circuit comprising a glow discharge device, means for supplying energy thereto, a control circuit therefor whereby the frequency of oscillation thereof is maintained at a sub-audio frequency, and means for impressing energy derived from the oscillations thereof on said thermionic tube whereby to produce corresponding variations in the energy supplied to said first mentioned oscillating circuits.

11. A stabilized oscillating circuit arrangement comprising a glow discharge device, a voltage supply circuit therefor, a control circuit therefor, said control circuit comprising both capacity and inductance, said glow discharge device being common to both circuits, one of said other elements at least being located solely within said control circuit, the relationship of said capacity and said inductance to said glow discharge device being such as to stabilize the frequency of oscillation of said system over a comparatively wide range of variations in impressed voltage.

WINSTON EDWARD KOCK. 

